Remove unused docs images

[Eric-Arellano]

These are all unused. Determined by running this script to run ripgrep:

import os
import subprocess

def rg_search(term):
    result = subprocess.run(['rg', term, "qiskit-metapackage", "qiskit-terra"], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
    return not bool( result.stdout)

with open("terms.txt", "r") as f:
    for line in f:
        term = line.strip() # Remove newline characters
        if rg_search(term):
            print(term)

With these terms:

aer.png
aqua.png
binary.png
contributor-flowchart.svg
favicon.ico
hardware.png
ignis.png
logo.png
metal.png
noise_cancel.png
qiskit.png
qiskit_main.svg
qiskit_nutshell.png
quantum_interference.png
system_error.png
system_one.jpeg
teleportation.png
teleportation_detailed.png
terra.png
getting_started_0.png
getting_started_1.png
ignis_overview.png
install_0.png
qiskit-framework.png

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This also moves two images from _static to images. There was no good reason to have them in separate folders. This change simplifies our setup.